The present invention relates to the field of hydrostatics, more particularly, hydraulic pistons used in the cylinder block of a hydrostatic power unit. The present invention relates to hollow or reduced oil volume pistons and methods of producing the same.
It is conventional to use solid steel pistons in the rotating cylinder block of a hydrostatic power unit. Solid steel pistons are durable, reliable, and inexpensive to make, but their weight tends to impose limitations on the speed of operation for the cylinder blocks in which they are used. They also develop more operational frictional forces.
Consequently, some manufacturers have constructed hollow pistons that weigh less than the solid steel pistons. One common and conventional method of making hollow pistons involves rough turning a hollow piston body and a separate piston cap from steel barstock. Then the body and cap are joined together by conventional welding techniques, such as inertia welding, to form a piston with a hollow interior. However, many fabrication steps with tight tolerances or process controls are required to make such welded hollow pistons, which makes them relatively costly to manufacture. Hollow pistons weigh less than solid pistons but don't necessarily reduce the compressed oil volume of the hydrostatic unit unless they are welded shut to enclose an internal void. Reduced compressible oil volume provides better control of swashplate moments and efficiency in swashplate controlled hydrostatic power units.
Therefore, a principal objective of this invention is the provision of an improved method for producing hollow pistons used in the cylinder block of a hydrostatic power unit.
Another objective of this invention is the provision of an easy and inexpensive method for producing hollow pistons.
Another objective of this invention is the provision of a method for producing hollow pistons by utilizing a unique combination of new and conventional metal injection molding techniques.
Another objective of this invention is the provision of a method for producing hollow pistons that involves the steps of securing a core insert of a non-metallic material in a mold, filling the mold with a mixture of non-metallic binding material and metal particles, then eradicating the non-metallic binding material to leave a void in the cast piston.
Another objective of this invention is the provision of a method for producing hollow pistons that reduces the number and difficulty of the subsequent machining operations required to finish the piston.
These and other objectives will be apparent to one skilled in the art from the drawings, as well as from the following description and claims.